Known in the art are processes for producing alkali salts of alkylsulphonic acids, wherein the alkyl contains 10 to 20 carbon atoms, comprising outgassing the reaction mixture obtained from sulphoxidation of n-paraffins having from 10 to 20 carbon atoms, taken either separately or in various combinations and consisting of corresponding alkylsulphonic acids, sulphuric acid, unreacted n-paraffins, sulphurous anhydride and water. Thereafter the outgassed reaction mixture is added either with aliphatic saturated monohydric alcohols having from 1 to 5 carbon atoms, or an alcoholic solution of an alkali.
In the former case (addition of alcohols) the resulting mixture is stratified into two layers, the upper layer comprising the unreacted n-paraffins contaminated with the alcohol and the lower layer comprising an aqueous-alcoholic solution of corresponding alkylsulphonic acids and sulphuric acid.
In the latter case (addition of an alcoholic solution of an alkali) the resulting mixture is stratified into three layers: the upper one comprises the unreacted n-paraffins contaminated with the alcohol; the middle layer is an aqueous-alcoholic solution of alkali salts of corresponding alkylsulphonic acids; the lower layer comprises an aqueous solution of alkali salts of sulphuric acid.
In the former case the lower layer is separated from the upper layer of the unreacted n-paraffins and neutralized with an aqueous alkali solution. The resulting neutralizate is, in turn, stratified into two layers, the upper one comprising an aqueous alcoholic solution of alkali salts of corresponding alkylsulphonic acids and the lower layer - an aqueous solution of alkali salts of sulphuric acid. The lower layer is separated from the upper layer, whereafter the desired product is recovered from the remaining upper layer in the form of a paste or a melt (i.e. in a molten condition) by means of evaporation or salting-out with a saturated solution of sodium chloride.
In the latter case the middle and lower layers are separated from the upper layer of the unreacted n-paraffins, whereafter operations similar to those of the former case are performed.
The alkali salts of alkylsulphonic acids prepared by conventional processes feature a high content of alkali salts of sulphuric acid (mineral impurities) within the range of from 4 to 16% by weight as calculated for solids.
Presence of mineral impurities in alkali salts of alkylsulphonic acids in increased amounts makes it impossible to utilize them as emulsifying agents in polymerization processes.
These prior art processes also have a disadvantage residing in that the recovered n-paraffins are contaminated with alcohol. Those n-paraffins cannot be recycled to the stage of sulphoxidation without resorting to purification thereof from the alcohol.